Guided radiation therapy system

ABSTRACT

A system and method for accurately locating and tracking the position of a target, such as a tumor or the like, within a body. In one embodiment, the system is a target locating and monitoring system usable with a radiation delivery source that delivers selected doses of radiation to a target in a body. The system includes one or more excitable markers positionable in or near the target, an external excitation source that remotely excites the markers to produce an identifiable signal, and a plurality of sensors spaced apart in a known geometry relative to each other. A computer is coupled to the sensors and configured to use the marker measurements to identify a target isocenter within the target. The computer compares the position of the target isocenter with the location of the machine isocenter. The computer also controls movement of the patient and a patient support device so the target isocenter is co-incident with the machine isocenter before and during radiation therapy.

TECHNICAL FIELD

[0001] This invention relates generally to radiation therapy systems,and more particularly to systems and methods for accurately locating andtracking a target in a body to which guided radiation therapy isdelivered.

BACKGROUND OF THE INVENTION

[0002] Recent advances in radiation therapy are providing new avenues ofeffective treatment for localized cancer. These includethree-dimensional conformal external beam radiation, intensity modulatedradiation therapy (IMRT), and stereotactic radiosurgery andbrachytherapy. These newer treatment modalities deliver greater doses ofradiation to the tumor, which accounts for their increased effectivenesswhen compared to standard external beam radiation therapy.

[0003] To achieve continued improvements in the management of localizedcancers with radiotherapy, further dose escalation is necessary becausea dose response relationship for radiotherapy exists for most cancers.However, with the increased dose of delivered radiation comes thepotential for increased complications to healthy tissues, unlessmeasures are taken to reduce the amount of adjacent normal tissueirradiated. Effective radiation treatments are dependent upon both totaldose of radiation and the volume of normal tissue irradiated around thetumor. Therefore, as the radiation dose is increased, the volume ofadjacent normal tissue irradiated must be decreased in order to keep anequivalent rate of effective radiation treatment.

[0004] To reduce the amount of adjacent normal tissue that isirradiated, one must prescribe the radiation to the target with atighter treatment margin, that being an area of healthy tissue aroundthe target that receives the full dose of prescribed radiation. Forexample, if the treatment margin for prostate cancer is too large, themargin may encompass some rectal, bladder and bulbar urethral tissues.It is highly desirable to provide a margin that does not encompass theseimportant tissues.

[0005] It would be ideal to have no treatment margin at all. Some marginhas been necessary, however due to day-by-day variability in the initialradiation treatment setup and delivery with existing systems. Marginshave also been needed to accommodate for potential internal movement ofa target within the patient's body that can occur even when the exteriorportion of the patient remains stationary. Several studies havedocumented and quantified that tumor motion in the prostate occursduring radiation treatment, primarily due to the patient's breathing,and due to natural rectal and bladder filling and emptying. Without sometreatment margin, the potential exists that the tumor itself could moveout of the treatment volume.

[0006] In addition, if the patient is set up so the radiation beam isinitially off target, or if the target moves during treatment, the beamhits more of the normal tissue and causes increased collateral damage tothe normal tissue, as well as potentially under-dosing the target. It ishighly desirable to prevent as much collateral damage to normal tissueas possible. Thus, day-by-day, minute-by-minute changes in radiationtreatment setup and target motion have posed serious challenges whendose escalation is attempted with current patient setup processes.

[0007] Current patient setup procedures are reliant upon alignment ofexternal reference markings on the patient's body with visual alignmentguides for the radiation delivery device. As an example, a tumor isidentified within a patient's body with an imaging system, such as anX-ray, computerized tomography (CT), magnetic resonance imaging (MRI),or ultrasound system. The approximate location of a tumor in the body isaligned with two or more alignment points on the exterior of thepatient's body, and external marks are written on the patient's skin tomark the alignment points.

[0008] During the patient setup for radiation treatment, the externalmarks are aligned with a reference system of the radiation deliverydevices. This setup process attempts to accurately position thetreatment target (or patient) isocenter within the body at a position inspace where the radiation beam is focused, known as the machineisocenter. By precisely positioning the treatment target with respect tothe machine isocenter, the effective patient treatment volume within thebody is accurately registered (or positioned) to the radiation therapytreatment plan location. If, however, the target has moved relative tothe external marks, then the target may be offset from the machine'sisocenter, even when the external aligning devices and marks areproperly aligned. Accordingly, the doctors and technicians cannot tellhow far the target has actually moved relative to the machine'sisocenter. As an example, studies have documented target displacementsof up to 1.6 cm between two consecutive days of prostate radiotherapytreatment. Substantial target displacement of lung tumors in a veryshort time period has also been documented because of the patient'sbreathing and heartbeats. Such internal motion of the target can causeinaccuracies in treatment deliveries, so larger margins of healthytissue are prescribed and irradiated to compensate for likely internaltarget motions.

SUMMARY OF THE INVENTION

[0009] Under one aspect of the invention, a system and methods areprovided for accurately locating and tracking the actual position of atarget within a body in preparation for and during radiation therapy. Inone embodiment, the system is usable with a radiation delivery sourcethat delivers a selected dose of radiation to the target in the bodywhen the target is positioned at the machine isocenter of the radiationdelivery source. The system includes a marker fixable in or on the bodyat a selected position relative to the target, such as in or near thetarget. The marker is excitable by an external excitation source toproduce an identifiable signal while affixed in or on the body. A sensorarray with a plurality of sensors is provided external of the body, andthe sensors are spaced apart in a known geometry relative to each other.

[0010] A data-processing unit is coupled to the sensor array and isconfigured to use the measurements from the sensors to determine theactual location of the marker and a target isocenter within the targetrelative to the sensors. A reference marker is also coupled to theradiation delivery device at a known position relative to the device'smachine isocenter. The reference marker provides a measurable signal fordetermining the position of the reference marker and the machineisocenter relative to the sensor array. The data-processing unit isconfigured to compare the position of the target isocenter with theposition of the machine isocenter in real time to determine whether thepatient is properly setup for the radiation therapy.

[0011] Under another aspect of the invention, a monitoring system iscoupled to the data-processing unit and has a feedback portionconfigured to provide feedback information about the actual position ofthe target isocenter relative to the machine isocenter. In oneembodiment, the feedback portion provides a visual and/or numericrepresentation of the positions of the machine isocenter and targetisocenter relative to each other. This representation may then be usedto adjust the position of the target isocenter before or during therapy.In another embodiment, the feedback portion provides a visual and/ornumeric display of the real-time movement of the target isocenterrelative to the machine isocenter. Additionally, the feedback data maybe used to automatically alert the operator of patient or targetmovement beyond acceptable limits. In a third embodiment, the feedbackdata may be used to automatically adjust, gate or shutoff the radiationtherapy treatment for normal (i.e. respiration) or unplanned patientmotion.

[0012] Under another aspect of the invention, an adjustable patientsupport assembly is combined with the tracking and monitoring system foruse with the radiation delivery system. The support assembly includes abase, a support structure movably attached to the base, and a movementcontrol device connected to the support structure in order toselectively move the support structure relative to the base. Theplurality of sensors spaced apart from each other are coupled to thebase in a fixed location relative to the base. The data-processing unitis coupled to the sensors to receive the signal measurement data fromone or more markers in or next to the target. The data-processing unitis configured to use the signal measurement data for each marker todetermine the actual location of the marker and target isocenter withinthe target. The data-processing unit is configured to identify thelocation of the target isocenter relative to the machine isocenter. Themovement control device is coupled to the data-processing unit and isadapted to position the target isocenter coincident with the machineisocenter in response to data from the data processing unit.

[0013] Under another aspect of the invention, a method is provided fordelivering radiation therapy on a selected target within a body. Themethod includes positioning an excitable marker at a selected positionrelative to the target, exciting the implanted marker with an excitationsource external of the body to produce an identifiable marker signal andmeasuring the marker signal from the marker with a plurality of sensorsexterior of the body, positioned in a known geometry relative to eachother. The method also includes determining the location of the markerand a target isocenter in the body relative to the sensors based uponthe measurements of the marker signal from the sensors. The methodfurther includes determining the location of a machine isocenter of theradiation delivery assembly relative to the sensors and relative to thetarget isocenter, and positioning the body relative to the radiationdelivery device so the target isocenter is coincident with the machineisocenter. Radiation therapy is then applied from the radiation deliverydevice to the treatment volume about the target isocenter.

[0014] In yet another aspect of the invention, a method is provided forpositioning a body relative to a radiation delivery device fordelivering radiation therapy to a treatment volume at a target isocenterwithin the body. The body has a selected target therein, and at leastone excitable marker is positioned in a known position relative to thetarget. The method includes positioning the body on a movable supportassembly adjacent to a plurality of sensors, and energizing theexcitable marker with an excitation source exterior of the body. Theexcited marker provides an identifiable marker signal. The marker signalis measured with the plurality of sensors positioned exterior of thebody and in a known geometry relative to each other and relative to themovable support assembly. The location of the marker and a targetisocenter within the treatment volume is determined based on themeasurements by the sensors of the marker signal. The location of thetarget isocenter is also determined relative to the plurality of sensorsand relative to the machine isocenter. The location of the targetisocenter is compared to the location of the machine isocenter, and ifthe two isocenters are not coincident with each other, a portion of thesupport assembly moves the body and target to position the targetisocenter coincident with the machine isocenter.

BRIEF DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a schematic side elevation view of a target locating andmonitoring system in accordance with an embodiment of the presentinvention. Excitable markers are shown implanted in or adjacent to atarget in a patient's body, a sensor array is shown exterior of thepatient, and a radiation delivery device is shown in a position to applyradiation therapy to the target within the body.

[0016]FIG. 2 is a schematic top plan view of the patient on a movablesupport table, with the implanted markers, the target, and the sensorarray shown in hidden lines.

[0017]FIG. 3 is an enlarged side elevation view of one embodiment of asingle-axis marker usable in the system illustrated in FIG. 1.

[0018]FIG. 4 is an enlarged side elevation view of one embodiment of athree-axis marker usable in the system of FIG. 1.

[0019]FIG. 5 is an enlarged isometric view of another embodiment of athree-axis marker usable in the system of FIG. 1.

[0020]FIG. 6 is an enlarged partial schematic isometric view of thetarget, three markers implanted in or near the target, an externalexcitation source, the sensor array, and a computer controller in thesystem of FIG. 1.

[0021]FIG. 7 is a schematic isometric view of an alternate embodiment ofthe sensor array in the system of FIG. 1.

[0022]FIG. 8 is a geometric representation of two intersecting spheresrepresenting data for determining a marker's position relative to twosensors.

[0023]FIG. 9 is a geometric representation of four intersecting spheresrepresenting data for determining a marker's position relative to foursensors.

[0024]FIG. 10 is a schematic isometric view of a target in a body shownin phantom lines in a first position and shown in solid lines in asecond, different position within the body.

[0025]FIG. 11 is an enlarged isometric view of the monitoring system ofFIG. 1 showing a simulated target, simulated markers, and a simulatedtarget isocenter shown in phantom lines on a display screen, and actualmarker locations and target isocenter locations shown in solid lines onthe display screen.

[0026]FIG. 12 is an isometric view of the monitoring system of FIG. 11with the simulated and actual markers shown aligned with each other, andthe machine isocenter and target isocenter coincident with each other.

[0027]FIG. 13 is a simulated isometric view of a target and markersillustrated on the monitoring system, and the target is shown in a firsttarget condition.

[0028]FIG. 14 is a simulated isometric view of the target and markers ofFIG. 13, and the target is shown in a second condition representing achange in the target size or condition relative to the markers.

[0029]FIG. 15 is a side elevation view of an alternate embodiment of thepresent invention with surface markers mounted to an external surface ofthe patient's body and in alignment with each other and the target.

[0030]FIG. 16 is a top plan view of all of the patient with thesurface-mounted markers of FIG. 15 mounted thereon.

[0031]FIG. 17 is a schematic flow diagram of a radiation deliveryprocess for delivering radiation treatment to a target utilizing thesystem of FIG. 1.

DETAILED DESCRIPTION

[0032] FIGS. 1-17 illustrate a system and several components forlocating, tracking and monitoring a target within a body in accordancewith embodiments of the present invention. The system and components areusable to locate, track, monitor, and evaluate a target for applicationof a selected therapy to the target, such as guided radiation therapy.Several of the components described below with reference to FIGS. 1-17can also be used in systems for performing methods in accordance withaspects of the present invention. Therefore, like reference numbersrefer to like components and features throughout the various figures.

[0033] Referring to FIGS. 1 and 2, one aspect of the present inventionprovides a system 10 configured for use in applying guided radiationtherapy to a target 12, such as a tumor, within the body 14 of a patient16. The system 10 allows the target 12 to be located within thepatient's body 14 and the actual position monitored in real time whileapplying ionizing radiation therapy to the target from a radiationdelivery source 18. The target 12 may move within the body 14 because ofbreathing, organ filling or emptying, or other internal movement. Thetarget motion is tracked and monitored relative to the radiation beam toinsure accurate delivery of radiation to the target 12 and, if needed,only a minimum margin around the target. While the system 10 isdiscussed below in connection with guided radiation therapy forradiation of a tumor or other target, the system can be used fortracking and monitoring other targets within a body, such as for othertherapeutic or diagnostic purposes.

[0034] The radiation delivery source 18 of the illustrated embodiment(FIG. 1) is an ionizing radiation device, known as a linear accelerator,but could be any radiation therapy delivery device. Other radiationtherapy delivery devices can be used, including such devicesmanufactured by Varian Medical Systems, Inc. of Palo Alto, Calif.;Siemans Medical Systems, Inc. of Iselin, N.J.; Electa Instruments, Inc.of Iselin, N.J.; or Mitsubishi Denki Kabushik Kaisha of Japan. Suchdevices are used to deliver conventional single or multi-field radiationtherapy, 3D conformal radiation therapy (3D CRT), inverse modulatedradiation therapy (IMRT), stereotactic radiotherapy, and tomo therapy.This is done in conjunction with a variety of treatment planningsoftware systems.

[0035] The radiation delivery source 18 delivers a gated, contoured orshaped beam 19 of ionizing radiation from a movable gantry 20 to a areaor volume referenced to a point at a location away from the gantry. Thispoint in space, referred to as a machine isocenter 22, is the point towhich the ionizing radiation beam 19 is configured about as determinedby industry standard treatment planning processes. The system 10 allowsthe target 12 to be accurately positioned at the machine isocenter 22 sothe ionizing radiation is accurately delivered to the target 12. Thesystem also allows the target's actual position relative to the machineisocenter 22 to be monitored during the radiation therapy so as tominimize collateral damage to healthy tissue surrounding the target.

[0036] The illustrated system 10 includes a plurality of markers 30positioned in or adjacent to the target 12 to mark the target's actuallocation in the body 14. Accordingly, the markers 30 are markers in, onor near the body. In one example, the markers 30 may be attached topatient-immobilization devices at known locations relative to thetreatment isocenter. The markers 30 are energized or excited by anexcitation source 32 positioned exterior of the patient's body 14. Whenthe markers 30 are excited, they each resonate at a selected uniquefrequency and generate a low energy radio-frequency magnetic signalmeasurable from outside of the body 14. The signals from the markers 30are detected and measured by an array 34 of sensors 36 located exteriorof the patient's body 14. The sensors 36 are positioned in a fixed,selected geometry relative to each other, so the array 34 defines afixed reference coordinate system from which location and movement arecalculated. The sensors 36 are operatively coupled to a computercontroller 38 that receives the measurement information from each sensorand determines the actual location of the markers 30 within thepatient's body 14 relative to the sensors.

[0037] In one embodiment, the computer controller 38 includes algorithmsused to define and determine the location of the target isocenter 40within the target 12, based upon the signal measurements by the sensors36 from the resonating markers. In another embodiment, the location ofthe target isocenter 40 within the target 12 is selected, and thecomputer controller 38 utilizes position information about the positionand/or orientation of each marker 30 relative to the selected targetisocenter. The target isocenter 40 is the point or position within thetarget to which the shaped dose of radiation is configured around orreferenced to as determined by a treatment planning process. In oneembodiment, the sensors 36 are polled twelve or more times per minute totrack the actual position of the target isocenter 40 within thepatient's body 14 relative to the sensor array 34. Accordingly, theactual position of the target 12 and the target isocenter 40 can bemonitored in real time when the patient is positioned adjacent to thesensor array 34.

[0038] The actual position of the target isocenter 40 is compared to theposition of the machine isocenter 22 relative to the sensor array 34.The illustrated system 10 has a reference device 42 positioned on thegantry 20 of the linear actuator or another selected position on aradiation therapy delivery device used in alternate embodiments. Inthese alternate embodiments, the other radiation therapy delivery devicecan include cobalt machines, a Gamma Knife, a Cyberknife, specializedstereostatic radiotherapy devices, or a TomoCT assembly (which utilizesa linear actuator in a CT scanner). The reference device 42 ispositioned at a known spatial or geometric relationship relative to themachine isocenter 22. The reference device 42 in one embodiment is aresonating, three axis, single frequency marker that provides ameasurable signal detectable by the sensors 36 in the array 34. Thereference device 42 in alternate embodiments can be positioned in aremote location away from the gantry 20. In either embodiment, thelocation of the machine isocenter 22 relative to the sensor array 34 canbe calculated upon determining the position of the reference device 42relative to the sensor array. The sensors 36 provide the measurementdata about the reference device 42 to the computer controller 38, andthe computer controller calculates the location of the machine isocenter22 relative to the sensor array 34.

[0039] The location of the target isocenter 40 relative to the sensorarray 34 is compared to the position of the machine isocenter 22relative to the sensor array. If the target isocenter 40 and machineisocenter 22 are spatially misaligned such that the two isocenters arenot three-dimensionally coincident with each other, the patient 16,and/or target 12 can be moved relative to the machine isocenter 22. Thetarget 12 position is moved until the target isocenter 40 is coincidentwith the machine isocenter 22. Once the target and machine isocenters 40and 22 are acceptably aligned, the radiation delivery source 18 can beactivated to provide the ionizing radiation beam 19 referenced to thetarget isocenter, thereby irradiating the target according to aradiation treatment plan, while minimizing or eliminating collateraldamage to healthy tissue surrounding the target 12. The actual locationof the target isocenter 40 can also be monitored in real time during theradiation therapy to ensure that the target isocenter does not move anunacceptable amount relative to the machine isocenter 22 and allow fortreatment when the treatment isocenter and the machine isocenter arewithin acceptable displacement limits.

[0040] In the illustrated embodiment, the system 10 also includes amonitoring assembly 44 coupled to the computer controller 38 thatprovides feedback data to a user interface for the doctor or technicianoperating the system and/or the radiation delivery device 18. As anexample, the monitoring assembly 44 can provide the feedback data as avisual representation of the target isocenter's position inthree-dimensional space relative to the machine isocenter's position inreal time as the patient is being set up and positioned for theradiation therapy. The monitoring assembly 44 can also provide otherfeedback data to the user interface including, for example, confirmationof setup completion, graphical information, patient information,radiation treatment plan information, or other information that can beutilized during the guided radiation therapy process.

[0041] FIGS. 3-5 illustrate excitable markers 30 of alternateembodiments usable in the system 10. One of the markers 30 shown in FIG.3 is an implantable, single-axis, resonating marker 31 having a ferritecore 46 wrapped by a conductive winding 48, and the winding is connectedto a small capacitor 50. The marker 31 is configured to be energized bythe external excitation source 32, which produces an electromagneticfield. This electromagnetic field causes the marker 31 to resonate at apredetermined frequency, thereby providing a signal of sufficientintensity to be measured by the sensors 36 (FIG. 1) from outside of thebody. A biologically inert coating 52 encapsulates the ferrite core 46,the winding 48, and the capacitor 50 so as to provide a small,self-contained, wireless excitable marker 31 that can be permanentlyimplanted into the patient. In this embodiment, the marker 31 is“wireless” because it need not be physically connected via wires to anoutside energy source for generation or communication of the markersignal. In one embodiment, the marker 31 has a length of onlyapproximately 5 mm and diameter sized to fit through an applicatorneedle. The marker 31 in other embodiments can have different sizes asneeded for the desired configuration of the marker signal.

[0042] As best seen in FIG. 4, another one of the excitable markers 30includes a three-axis, wireless, resonating marker 52 with threesignaling portions 54. Each signaling portion 54 is positioned axiallyperpendicular to the other two signaling portions. Accordingly, thethree signaling portions 54 define an X, Y, Z reference coordinate. Eachof the signaling portions 54 includes a ferrite core 46, a winding 48around the ferrite core, and a small capacitor 50 connected to eachwinding. Each signaling portion is configured to be energized by theexternal excitation source 32, and to resonate at a frequency differentthan the resonating frequency of the other two signaling portions.

[0043] In one embodiment, as illustrated in FIG. 4, the three-axismarker 52 includes a biologically inert coating 56 that encapsulates allthree of the signaling portions 54, so the marker can be permanentlyimplanted in the patient's body. When the marker 52 is energized by theexternal excitation source 32, each of the marker's signaling portionsresonates at its selected frequency and provides the measurable markersignal at an intensity so it can each be measured by the sensor array 34(FIG. 1). Frequency multiplexing by the computer controller allows thecomputer controller 38 to differentiate between the marker signals fromthe different signaling portions of the marker when calculating themarker's position and orientation relative to the sensor array.

[0044] As best seen in FIG. 5, another embodiment of the marker 30includes a cube-shaped marker 58 with a single ferrite core 60 and threesets of windings 62 axially oriented perpendicular to each other todefine the X, Y, and Z axes for the marker. Each winding 62 is connectedto a small capacitor 64 and configured to resonate at a frequencydifferent than the other two windings. Accordingly, the cube-shapedmarker 58 is also a wireless, three-axis, resonating marker.

[0045] In one embodiment, the wireless, excitable markers 30 areconfigured to resonate and provide a measurable signal within thefrequency range of approximately 10 kHz to 200 kHz, inclusive. In otherembodiments, the markers 30 can be self-contained, powered markers thatinclude a power source, such as a battery, that provides sufficientpower to produce the measurable identifiable marker signal. In otherembodiments, the markers 30 can be “wired” markers connectable via wiresto a selected power or excitation source to allow the markers togenerate the unique marker signal. The marker signal can be unique as afunction of frequency (i.e., frequency multiplexing) as a function oftime or time multiplexing.

[0046] In selected applications, a single marker 31, preferably asingle-axis marker, is implanted in the target 12, and the intensity ofthe signals from the single resonating marker is used to determine thetarget location information relative to the sensor array 34. Inalternate embodiments, two, three, or more markers 30 are implanted atknown locations in or adjacent to the target. Each marker 30 producesits unique signal relative to the other markers, so the sensor array 34differentiates between the markers by frequency multiplexing. The sensorarray 34 measures the intensity of the unique signals from the markers30. The signal intensity measurements are converted for use in geometriccalculations (discussed in greater detail below) to accurately determinethe actual three-dimensional location (X, Y, Z) and possibly the angularorientation (pitch, yaw, roll) of the marker relative to the sensorarray 34.

[0047] Referring again to FIG. 1, the system 10 includes the excitationsource 32 that generates a magnetic field for exciting the markers 30.The excitation source is positioned in a selected location relative tothe target 12 and close enough to the markers 30 so the emitted magneticfield has sufficient intensity to acceptably energize the markers. Inthe illustrated embodiment, a plurality of markers 30 are permanentlyimplanted within the patient's body 14 in or adjacent to the target 12.In one embodiment, the computer controller 38 provides a separate drivercircuit for the excitation source 32 for each marker 30, so as toselectively excite the respective marker at the selected frequency. Theexcitation source 32 in one embodiment is a three-dimensional, ACmagnetic field source that generates three-dimensional magnetic fieldsin the X, Y, and Z axes. This excitation source 32 provides one sourcecoil for each marker 30, and the electric current driven through thesource coil generates the AC magnetic waveform tuned for the respectivemarkers. In another embodiment, the source coil (or coils) in theexcitation source 32 is provided by a coil configured to generate themultiple or scanned excitation frequency fields for the respectivemarkers 30.

[0048]FIGS. 6 and 7 are schematic isometric views of sensor arrays 34positionable exterior of the body (FIG. 6) and spaced apart from themarkers 30 positioned in or near the target 12. In these illustratedembodiments, three markers 30 are shown implanted in or near the target12. As seen in FIG. 6, the sensor array 34 includes a frame 70 thatsupports a plurality of sensors 36 in a fixed and known geometryrelative to each other along X, Y, or Z axes of a reference coordinatesystem 72. The position of each sensor 36 on the frame 70 relative tothe reference coordinate system 72 is fixed and defines fixed referencepoints for obtaining measurement data used by the computer controller38. In the embodiment of FIG. 6, the frame 70 supports the sensors 36 sothe sensors are positioned in a single plane. In the embodiment of FIG.7, the frame 70 is shaped to support the sensors 36 in two orthogonalplanes, so the sensors 36 are oriented along the X, Y, and Z axes of thereference coordinate system 72. Accordingly, the sensor array 34provides the fixed reference structure from which measurements are takenand calculations performed to determine the relative positions of thetarget 12, the target isocenter 40 and the machine isocenter 22.

[0049] The illustrated embodiments of FIGS. 6 and 7 utilize “wireless”markers 30, so frequency multiplexing is utilized to distinguish thesignals from the different markers. Each sensor 36 is a three-axissensor that measures the absolute marker signal strengths from arespective one of the markers 30 relative to the X, Y, and Z axes. Theabsolute signal strength of the marker signal along each axis in thereference coordinate system 72 is measured by the sensors 36 for eachmarker in order to determine the X, Y, and Z position of each marker.

[0050] It is known that the strength of a magnetic field decreases at aratio proportional to the cube of the distance from the source.Accordingly, the distance of the marker from the sensor can bedetermined based upon the marker's signal strength. The geometricrelationship from the marker to a series of sensors that are spaced atknown locations relative to each other is used to solve a series ofequations with one unique result. Accordingly, the distance between themarker 30 and the sensor 36 calculated by the computer controller 38based on the marker's signal strength measured by the respective sensorsand iterated for a best fit solution to the geometric equations.

[0051] The precise location of a marker 30 in space relative to thesensor array 34 can be calculated based upon the distances between thatmarker and at least four separate three-axis sensors spaced apart fromeach other in the array. The absolute magnitude of the distance from thethree-axis sensor is determined by squaring the each of the three axismagnitudes (x, y, and z orientations), adding the results and finallytaking the square root for the distance resultant. As an example, thedistance between one sensor 36 and one of the markers 30 correspondsgeometrically to the radius of a sphere. FIG. 8 shows two illustrativespheres 100 with the center points 102 each defined by a separate sensor36. When two spheres 100 intersect, the intersection defines a circle104. So, it is known that the marker is located at some point on thatcircle. When three spheres 100 intersect, shown in FIG. 9, theintersection defines one of two points 105 where the marker is locatedon that line. When four spheres 100 intersect, the intersection definesa single point 108 in space corresponding to the precise position of themarker 30 in space relative to the sensor array 34.

[0052] In an embodiment using a single marker 30 implanted in a target12, the sensor array 34 can include only four three-axis sensors 36 todetermine that marker's position in space. Since the signals arefrequency multiplexed and multiple frequencies may be received with eachsensor coil and each individual frequency component may be examined byprocessing the combined signal with a fast Fourier transform (FFT) inthe control electronics, multiple markers may be located with the samesensors. In the embodiments with three or more markers 30 positioned inor near the target 12, the sensor array 34 is configured at knowngeometric orientations relative to the reference coordinate system 72,so that the marker signal measurements can be used by the computercontroller 38 to calculate the angular orientation of the treatmentvolume (i.e., the pitch, yaw and roll) in space relative to thereference coordinate system 72 by using the three sets of threedimensional data (x, y, and z from the single axis markers). Based uponthe position of the markers 30 relative to the target, the location andangular orientation of the target 12 can be determined by the computercontroller 38.

[0053] The marker signal may be separated from the signal generated bythe excitation source 32 via signal processing software or electronicsin a number of ways. In one embodiment, the excitation source 32 isturned or gated “on” to excite the marker and then turned or gated “off”to allow for measurement of the marker response without interference bythe signal from the excitation source. The marker 30 will continue toresonate after the excitation source 32 is gated “off” for a perioddetermined by the sensor's electric inductance, capacitance and seriesresistance. In another embodiment, the system is operated in continuouswave (CW) mode where the excitation source 32 remains “on” duringmeasurement of the markers 30. The marker signal is 90 degrees “out ofphase” with the signal from the excitation source, so the marker signalis removed from the excitation signal. The time of the zero crossing ofthe excitation signal is known and the remaining marker signal will beat its peak intensity at that time. In a third embodiment, the outputfrequency of the excitation source's signal is continuously varied orscanned to maximize the excitation of the markers 30 which results in amaximum marker signal while minimizing or eliminating unwantedexcitation signal.

[0054] The position of each marker 30 relative to the target 12 andrelative to the target isocenter 40 is also calculated or determined. Inone embodiment, the target isocenter 40 in the target 12 is chosen firstbased upon imaging data about the target provided by an imaging system,such as a CT scan, MRI, ultrasound system, or nuclear imaging system(e.g. positron emission tomography). Once the target isocenter 40 isselected, the position of each implanted marker 30 is measured relativeto the target isocenter 40. The position of the target isocenter 40 isthen determined relative to the reference coordinate system 72 basedupon defining the location of each marker 12 relative to the referencecoordinate system.

[0055] In another embodiment, the target isocenter 40 is defined as afunction of the marker locations relative to the target 12. The markers30 are selectively positioned in or near the target 12 and theorientation of the markers is used to define and calculate the targetisocenter. Thus, the target isocenter 40 within the target 12 can bedefined and its position determined relative to markers 30 and thereference coordinate system 72 even if the markers 30 are not actuallyimplanted within or even immediately adjacent to the target 12. Themarkers 30 are, however, positioned close enough to the target 12 sothat if the target moves, the target and markers move togethersubstantially as a unit. Therefore, movement of the target 12 ismonitored by tracking movement of the markers 30 relative to the sensorarray 34.

[0056] The system 10 is configured to track motion of the target 12 inreal time. When the portion of the patient's body 14 containing thetarget 12 and markers 30 is positioned adjacent to the sensor array 34and the markers are energized, the computer controller 38 acquires datafrom each sensor 36 and outputs a result approximately 12 times persecond. The computer controller obtains measurement data from thesensors 36 and calculates the location of the target isocenter 40relative to the sensor array every five seconds. In alternateembodiments, the computer controller 38 can measure the sensors 36 tomonitor in real time the motion of the particular target isocenter 40relative to the sensor array 34. The measurement update rate may bereduce as to allow for sufficient data averaging to reduce themeasurement noise at the same time allowing for an adequate update ratefor the user.

[0057]FIG. 10 is a partial isometric view illustrating an aspect of thepresent invention that includes a support table 76 that movably supportsthe patient's body 14 under the gantry 20 and adjacent to the sensorarray 34. The support table 76 is positionable below the machineisocenter 22. The support table 76 is movable to adjust the position ofthe patient 16 relative to the machine isocenter 22 until the targetisocenter 40 is coincident with the machine isocenter. The sensor array34 may be placed on, under, or connected to the support table 76.Alternatively, it may be mounted to the linear accelerator's gantry at alocation sufficiently close to any markers 30 (implanted, external organtry) that are to be located. In this alternate embodiment with thesensor array 34 mounted to the linear accelerator, the position from themachine isocenter 22 to the sensor array will be known, so that aseparate gantry marker 42 may not be used.

[0058] As best seen in FIGS. 1 and 10, the support table 76 has a base88 and a tabletop 90 movably supported to the base for linear andangular movement relative to the sensor array 34. A movement controlsystem 78 is connected to the tabletop 90 to control movement of thetabletop and the patient 16 relative to the machine isocenter 22 and thesensor array 34. The control system 78 is also coupled to the computercontroller 38, and the computer controller 38 is programmed to activatethe control system 78 to adjust the linear or angular position of thepatient. In one embodiment, the tabletop's position moves in response toan authorized user such as doctor, physicist or technician activatingthe control system, or automatically in response to instructionsprovided by the computer controller 38.

[0059] Once the target 12 is positioned so the target isocenter 40 iscoincident with the machine isocenter 22, ionizing radiation can beselectively and very accurately delivered directly to the target area orvolume. Application of the radiation therapy to the target 12, can beprovided at the selected dosage and intensity with precise accuracy,while potentially minimizing the margin needed around the target. In oneembodiment, the actual position of the target isocenter 40 issubstantially continuously monitored and tracked relative to the machineisocenter 22 during delivery of the radiation therapy. If the targetisocenter 40 moves away from the machine isocenter 22 beyond anacceptable range of displacement distances, the computer controller 38provides a signal to the radiation delivery device to interrupt theradiation therapy to the target. The target's position can then beadjusted manually or automatically until the target isocenter 40 isagain coincident with the machine isocenter 22, and radiation therapycan resume. In one embodiment, the computer controller 38 is programmedso that if the target isocenter 40 moves from the machine isocenter 22,but the distance of movement does not exceed the acceptable range, thecomputer controller 38 will not interrupt the radiation therapy. Thisrange of movement is dependent upon many factors, such as the targettype (e.g., prostate, lung, liver), target size, target location, beamshape/size, and the radiation treatment plan.

[0060] Tracking of the target isocenter's position is facilitated by themonitoring assembly 44, which is coupled to the computer controller 38.FIGS. 11 and 12 illustrate a feedback portion 80 of the monitoringassembly 44 that provides feedback data to an operator about, as anexample, the position of the markers 30, the target isocenter 40 and themachine isocenter 22. The feedback portion 80 is a display monitor thatprovides pictorial, graphical, or textual information to the operator.Other feedback portions 80, such as graphical display devices, auditoryfeedback devices, or visual feedback devices can be used in alternateembodiments. In one embodiment, the computer controller 38 containsimaging data, such as from a CT, MRI, or ultrasound imaging system, thatdefines the shape and size of the target 12 within the body 14. Theimaging data also defines the locations of each marker 30 in or aroundthe target 12. The computer controller 38 uses the imaging data toprovide a simulated model of the target, the markers, and the targetisocenter. This simulated model is displayed on the feedback portion 80as shown in FIG. 11 in phantom lines. The simulated model is alsodisplayed overlaying the machine isocenter 22, so the simulated targetisocenter 40 is coincident with the machine isocenter. The simulatedtarget and simulated markers can also display how the actual targetneeds to be positioned and oriented three-dimensionally for theparticular radiation therapy to be applied to the target.

[0061] The monitoring assembly 44 also receives and displays informationfrom the computer controller 38 to show the actual locations of themarkers 30 and target isocenter 40 relative to the machine isocenter 22,and relative to the simulated target and markers. Accordingly, thefeedback portion 80 allows the operator to determine the actual positionof the markers relative to the simulated markers, and the targetisocenter 40 relative to the machine isocenter 22 substantially in realtime while the patient 16 is on the support table 76 (FIG. 1). Thepatient 16 and support table 76 can be repositioned until the target 12is properly oriented for the selected radiation therapy.

[0062] In addition to accurately tracking and monitoring the position ofthe target 12 relative to the machine isocenter 22, the system 10 isalso usable to monitor the status of the target, such as a tumor or thelike, in a patient's body 14 over time. FIGS. 13 and 14 are schematicviews showing a tumor 90 in a body 92. Three markers 30 are shown forthis embodiment permanently implanted in or adjacent to the tumor 90.Images of the tumor 90 and markers 30 are obtained by CT, MRI,ultrasound, or other imaging technique over time. From these multipleimages of the tumor 90 and markers 30, the position of the markersrelative to the tumor can be compared and tracked. Accordingly, a doctorcan use the markers 30 in the multiple images as a reference tool todetermine whether the tumor has shrunk, grown, moved, or otherwisechanged within the patient's body.

[0063] As an example, FIG. 13 illustrates an image of a tumor 90 in afirst condition with three markers 30 implanted therein, and FIG. 14illustrates a second image of the tumor taken later in time. The secondimage shows the same markers 30 in the same location within thepatient's body, and from the position of the tumor relative to themarkers, one can see that the tumor has shrunk. Thus, doctors can trackthe status of tumors or other targets within the body over time todetermine, as an example, the effectiveness of radiation therapy,whether additional treatments are needed, or whether a change in tumorgrowth has occurred or whether the radiation treatment plan needs to bealtered.

[0064] In the embodiments discussed above, the markers 30 are describedand shown as being subcutaneously implanted in or next to a target 12.This implantation of the markers 30 is performed when needed to ensurethat, if the target 12 moves, the markers will move with the target as aunit. In an alternate embodiment illustrated in FIGS. 15 and 16, themarkers are surface-mounted markers 110 adhered to the exterior surface112 of the patient's body 14 substantially adjacent to and in alignmentwith a target 12, in or on the body. The surface-mounted markers 110 canbe removably adhered with an adhesive, such as tape or the like, in asubstantially fixed location on the body's exterior surface 112 relativeto the target 12. These surface-mounted markers 110 are particularlysuitable for targets 12 known not to substantially move within the body14 relative to the exterior surface. The surface-mounted markers 30 arealso suitable for use when the target's size or location in the body 14is such that some motion of the target isocenter is not critical foreffective radiation therapy or treatment. Accordingly, thesurface-mounted markers 110 provide reference points for accuratealignment and orientation of the target 12 and the machine isocenter 22.Alternatively, markers 30 may be mounted on or in patient immobilizationdevices at known locations relative to the treatment isocenter.

[0065] The surface-mounted markers 110 in one embodiment are wirelessmarkers, so that the markers can remain adhered on the patient's body 14after a radiation treatment session so that the patient 16 can come andgo from the treatment area without disrupting the position of themarkers 110 relative to the target 12. In alternate embodiments, themarkers 110 remain adhered to the patient 16 and are connectable to leadwires of a “wired” marker system in the treatment area. The lead wirescan be disconnected from the markers 110 to allow the patient 16, toleave the treatment area while the markers remain fixed in place on thepatient's body.

[0066] The surface-mounted markers 110 are also usable to monitor apatient's base-line girth (anterior-posterior and lateral dimensions)during a radiation treatment program. The base-line girth measurements,referred to as patient separations, are initially obtained by CT, MRI,or physical measurements. Patient separations are used when preparing aradiation treatment plan for the patient. The surface-mounted markers100 can be utilized alone or in combination with implanted markers toprovide data about changes in the patient separations that may occurduring chemo radiotherapy. Each surface-mounted marker 110 has anidentifiable initial position in space relative to, as an example, thetarget isocenter or relative to each other. The sensor array 34 andcomputer controller 38 are configured to determine the distances betweeneach surface-mounted marker and/or the target isocenter. The computercontroller 38 calculates and monitors the distances, corresponding tothe patient separations. During the course of radiation treatment, ifthe patient separations change significantly, such as due to substantialweight loss from chemo or radiotherapy, the treatment plan may becomeinvalid because less patient tissue is available to alternate theradiation beam, thereby resulting in higher than planned doses ofradiation.

[0067] In one embodiment, the surface-mounted markers 110 are usable tofacilitate and speed up patient set-up procedures before and/or duringthe radiation therapy procedure. The surface mounted markers 110 arepositioned at selected locations on the patient's body 14 at knownpositions. The markers 110 are excited and the locations relative to thesensor array are determined. The marker's location information can thenbe used to calculate the Target Skin Distance or Source Skin Distance,which is the distance between the exterior skin of the patient and thelinear actuator or the tabletop. The markers 110 can also be used todetermine the tabletop-to-isocenter, which is the distance between thetabletop to the marker or other alignment means, such as lasercross-hairs projected on to the patient's skin. Accordingly, the surfacemounted markers 110 can be used to automatically calculate the relevantdistances during the set up procedure to quickly determine if thepatient is properly positioned in accordance with the radiation therapytreatment plan.

[0068] In another embodiment, the surface-mounted markers 110 can beused in conjunction with one or more markers 30 implanted in or near thetarget 12. The relative location of each marker 110 or 30 can becalculated and used for any combination of patient set-up, targetlocating, target positioning, target motion tracking, and/or targetevaluation, as discussed above.

[0069] The system 10 is also adapted for use in an automated patientsetup process prior to delivery of the radiation therapy. The automatedsetup process of one embodiment is shown schematically as a flow chartin FIG. 17. In this patient setup process, the tumor or other target inthe patient's body is identified (reference block 150). Images of thetarget are obtained (reference block 152), such as by X-rays, CT, MRI,nuclear imaging, or ultrasound imaging. The doctor and/or techniciansthen determine a treatment plan for the particular tumor (referenceblock 154). One or more markers are implanted in or on the body inselected positions relative to the target (reference block 156), and thelocation of the treatment isocenter relative to the markers isdetermined or calculated (reference block 158).

[0070] The patient is positioned on the movable support table so thetarget and markers are generally adjacent to the sensor array (referenceblock 160). The excitation source is activated to energize the markers(reference block 162), and the sensors measure the strength of thesignals from the markers (reference block 164). The computer controllercalculates location of the markers and the target isocenter relative tothe sensor array and the machine isocenter (reference block 166). Thecomputer compares the position of the target isocenter and machineisocenter (reference block 168), and if the two isocenters aremisaligned, the computer automatically activates the control system ofthe support table to move the tabletop relative to the machine isocenteruntil the target isocenter is coincident with the machine isocenter(reference block 170).

[0071] In one embodiment, the computer controller also determines theposition and orientation of the markers relative to the position andorientation of simulated markers. If the markers are not properlyaligned and oriented with the simulated markers, the support table isadjusted linearly and angularly as needed for proper marker alignment.This marker alignment properly positions the target volume along 6dimensions, namely X, Y, Z, pitch, yaw, and roll. Accordingly, thepatient is automatically positioned in the correct position relative tothe machine isocenter for precise delivery of radiation therapy to thetarget.

[0072] In one embodiment of this automated setup process, the computerrestricts the radiation delivery device from delivering the radiationbeam until the target isocenter is coincident with the machineisocenter. The computer monitors the position of the target isocenterduring delivery of the radiation treatment (reference block 172). If thetarget isocenter's position is outside a permitted degree or range ofdislocation, the computer interrupts the delivery of the radiationisocenter (reference block 174). The computer can then automaticallyreposition the tabletop and the patient (as a unit) so the target isproperly positioned with the target isocenter and is coincident with themachine isocenter (reference block 176), and the radiation therapy canbe reactivated for continued irradiation of the target (reference block178). If the delivery of the radiation therapy is not yet completed(reference block 180), the process returns to reference block 172 tomonitor the target's position relative to the machine isocenter as theradiation is being delivered. Accordingly, adjustments can be madeautomatically to ensure that the radiation is accurately delivered tothe target without requiring a large margin around the target.

[0073] Although specific embodiments of, and examples for, the presentinvention are described herein for illustrative purposes, variousequivalent modifications can be made without departing from the spiritand scope of the invention, as will be recognized by those skilled inthe relevant art. The teachings provided herein of the aspects of thepresent invention can be applied to locating, monitoring, and treating atarget within a body, and not necessarily limited to the illustrativeradiation treatment of the tumor in the body as described above.

[0074] In general, in the following claims, the terms used should not beconstrued to limit the invention to the specific embodiments disclosedin the specification and the claims, but should be construed to includeall target locating and monitoring systems that operate in accordancewith the claims to provide apparatus and methods for locating,monitoring, and/or tracking the position of a selected target within abody. Accordingly, the invention is not limited, except as by theappended claims.

1. A target locating and tracking system usable with a radiation therapydelivery source that delivers radiation to a target in a body, theradiation being delivered to a predetermined volume configured around amachine isocenter spaced apart from the radiation delivery source,comprising: a marker fixable at a position relative to the target in thebody, the marker being excitable by an external excitation source toproduce an identifiable marker signal from the marker while in the body;sensors spaced apart from each other in a known geometry relative toeach other and positioned to identify the marker signal from the marker,the sensors being configured to measure the marker signal and to providemarker measurement signals; a reference device positionable at aselected position relative to the radiation therapy delivery source andthe machine isocenter, the reference device configured to produce areference signal measurable by a plurality of the sensors; and a dataprocessing unit coupled to the sensors to receive the marker measurementsignals, the data processing unit being configured to use the markermeasurement signals to determine the location of the target volume witha target isocenter and the location of the reference device relative tothe plurality of sensors, and the data processing unit being configuredto identify the location of the target isocenter relative to the machineisocenter.
 2. The target locating and tracking system of claim 1,further comprising a plurality of markers implantable in the body, eachmarker being excitable by the excitation source to produce a uniquemarker signal measurable by the plurality of sensors.
 3. The targetlocating and tracking system of claim 2 wherein the plurality of markersincludes at least three markers.
 4. The target locating and trackingsystem of claim 3 wherein the markers are each axially misaligned witheach other.
 5. The target locating and tracking system of claim 2wherein the marker signal from each marker has a unique frequencydifferent from the frequency of other marker signals.
 6. The targetlocating and tracking system of claim 1 wherein the marker is a wirelessmarker implantable in the body.
 7. The target locating and trackingsystem of claim 6 wherein the data processing unit is configured todetermine the position of the target isocenter relative to the sensors.8. The target locating and tracking system of claim 1 wherein the markeris permanently implantable in the body.
 9. The target locating andtracking system of claim 1 wherein the marker is a single-axis,resonating marker.
 10. The target locating and tracking system of claim1 wherein the marker is a wireless marker.
 11. The target locating andtracking system of claim 1 wherein the reference device is measurable bya plurality of sensors.
 12. The target locating and tracking system ofclaim 1 wherein the data processing unit is configured to determine thelocation of the machine isocenter relative to the plurality of sensorsand relative to the treatment target isocenter based upon the signal ofthe linear accelerator reference.
 13. The target locating and trackingsystem of claim 1, further comprising an excitation source remote fromthe marker and configured to generate an excitation field that energizesthe marker.
 14. The target locating and tracking system of claim 1wherein the plurality of sensors are fixed to a base in the knowngeometry to form a sensor array.
 15. The target locating and trackingsystem of claim 1, further comprising a patient support structure shapedand sized to support the body, the plurality of sensors is mounted tothe patient support structure.
 16. The target locating and trackingsystem of claim 15 wherein the table structure has a base and atabletop, the base being in a fixed location relative to the sensors andthe tabletop being movably adjustable relative to the sensors.
 17. Thetarget locating and tracking system of claim 1, further comprising amonitoring system coupled to the data processing unit, the monitoringsystem having a feedback portion configured to provide feedbackinformation about the position of the target isocenter and the machineisocenter relative to each other.
 18. The target locating and trackingsystem of claim 17 wherein the feedback portion is a visual display. 19.The target locating and tracking system of claim 17 wherein the dataprocessing unit and monitoring system are configured to identify anddisplay movement in real time of the target and machine isocentersrelative to each other.
 20. The target locating and tracking system ofclaim 1 wherein the marker is one of a plurality of markers axiallymisaligned with each other, and the data processing unit is configuredto identify a three-dimensional spatial position and orientation of thetarget relative to the plurality of sensors and the machine isocenter.21. The target locating and tracking system of claim 1 wherein thereference device is at least one excitable marker mountable to theradiation therapy delivery source.
 22. The target locating and trackingsystem of claim 1 wherein the reference device is out of physicalconnection with the plurality of sensors and the data processing unit toprovide a wireless interconnection therebetween.
 23. A target locatingand monitoring system usable with a radiation therapy delivery sourcethat delivers radiation to a target in a body, the radiation beingdelivered to a treatment volume determined by a machine isocenter spacedapart from the radiation therapy delivery source, comprising: aplurality of markers fixable on or in the body at a known geometryrelative to each other and relative to the target, the markers eachbeing excitable by an external excitation source to produce anidentifiable marker signal from the marker while in the body; sensorsspaced apart from each other and positioned to measure the markersignals from the markerseach sensor being configured to provide markermeasurement signals for one or more of the markers; a reference devicepositionable at a selected position relative to the radiation deliverysource and the machine isocenter; and a data processing unit coupled tothe sensors to receive the marker measurement signals from the sensors,the data processing unit being configured to use the marker measurementsignals to determine the location of the target volume having a targetisocenter relative to the plurality of sensors, and the data processingunit being configured to identify the location of the target isocenterrelative to the machine isocenter.
 24. The target locating andmonitoring system of claim 23 wherein the signal from each marker has ameasurable signal, and each sensor measures the signal from at least oneof the markers, the computer controller being configured to determinethe location and/or spatial orientation of the target within the bodybased upon measurable signals.
 25. The target locating and monitoringsystem of claim 23, further comprising an excitation source remote fromthe markers and configured to operate an excitation field that energizesthe markers.
 26. The target locating and monitoring system of claim 23wherein the plurality of sensors are fixed to a base to define a sensorarray positionable as a unit at a selected position remote from themarkers.
 27. The target locating and monitoring system of claim 23,further comprising a patient support structure shaped and sized tosupport the body, the plurality of sensors being in a fixed positionrelative to a portion of the patient support structure.
 28. The targetlocating and monitoring system of claim 27 wherein the patient supportstructure has a base and a tabletop.
 29. The target locating andmonitoring system of claim 23, further comprising a monitoring systemcoupled to the computer controller, the monitoring system having afeedback portion configured to provide feedback information about theposition of the target isocenter and the machine isocenter relative toeach other.
 30. The target locating and monitoring system of claim 29wherein the feedback portion is a visual display.
 31. The targetlocating and monitoring system of claim 29 wherein the computercontroller and monitoring system are configured to identify and displaymovement in real time of the target and machine isocenters relative toeach other.
 32. The target locating and monitoring system of claim 23wherein the plurality of markers includes at least three markers. 33.The target locating and monitoring system of claim 23 wherein theplurality of markers are axially misaligned with each other.
 34. Aradiation therapy delivery system usable to irradiate a selected targetwithin a body, comprising: a radiation delivery assembly that deliversradiation from a radiation therapy delivery source to a machineisocenter spaced apart from the radiation delivery source; a markerfixable in or on the body at a position relative to the target, thebeing excitable by an external source to produce a measurable markersignal while in the body; a plurality of sensors spaced apart from eachother and positioned in a known geometry relative to each other, thesensors being configured to measure the marker signals and generatemarker measurement signals; a reference device coupled to the radiationtherapy delivery source and positioned remote from the machineisocenter; and a data processing unit coupled to the sensors to receivethe marker measurement signals, the data processing unit beingconfigured to use the marker measurement signals to determine thelocation of the target volume having a target isocenter and the locationof the reference device relative to the plurality of sensors, and thedata processing unit being configured to identify the location of thetarget isocenter relative to the machine isocenter.
 35. The radiationdelivery system of claim 34, further comprising a plurality of markersimplantable in the body, each marker being excitable by the externalsource to produce a marker signal measurable by the plurality ofsensors.
 36. The radiation delivery system of claim 35 wherein themarker signal from each marker is a unique signal different from theother marker signals.
 37. The radiation delivery system of claim 35wherein each marker signal has a frequency different from thefrequencies of other marker signals.
 38. The radiation delivery systemof claim 35 wherein the marker signal has a signal strength, and thedata processing unit calculates the spatial location of the markers andtarget isocenter based upon the marker signals.
 39. The radiationdelivery system of claim 34 wherein the reference device is mounted onthe radiation delivery assembly and provides a reference signalmeasurable by the sensors.
 40. The radiation delivery system of claim 34wherein the reference device provides a signal measurable by theplurality of sensors, the data processing unit is coupleable to thelinear accelerator reference device and the data processing unit isconfigured to identify the location of the machine isocenter relative tothe plurality of sensors based upon the measurements of the referencesignal.
 41. The radiation delivery system of claim 34, furthercomprising an excitation source positionable exterior of the body andconfigured to excite the marker to produce the marker signal.
 42. Theradiation delivery system of claim 34 wherein the plurality of sensorsdefines a sensor array positionable as a unit relative to the marker.43. The radiation delivery system of claim 34 further comprising apatient support structure shaped and sized to support the body in whichthe marker is implanted, and the sensors are mounted in a fixed locationrelative to a portion of the patient structure.
 44. The radiationdelivery system of claim 34 wherein the patient support structure has abase and a tabletop movably adjustable relative to the sensors forpositioning the target isocenter co-incident with the machine isocenter.45. The radiation delivery system of claim 34, further comprising amonitoring system having a feedback portion coupled to the dataprocessing unit and configured to provide feedback information about theposition of the machine isocenter and the target isocenter relative toeach other.
 46. The radiation delivery system of claim 34 wherein themarker is one of a plurality of markers, the markers each being axiallymisaligned with each other, and the computer controller being configuredto calculate a three-dimensional spatial position and orientation of thetarget relative to the plurality of sensors.
 47. The radiation deliverysystem of claim 34 wherein the radiation therapy delivery sourceincludes a movable gantry, and the reference device is mounted on thegantry at a position spaced apart from the plurality of sensors.
 48. Theradiation delivery system of claim 34 wherein the reference device is awireless excitable marker mounted to the radiation therapy deliverysource.
 49. The radiation delivery system of claim 34 wherein theradiation therapy delivery assembly is one of an intensity modulatedradiation therapy (IMRT) system, a three-dimensional conformal externalbeam radiation system, a stereotactic radiosurgery system, tomo therapyand a brachytherapy system.
 50. The radiation delivery system of claim34 wherein the data processing unit contains visual diagnostic dataidentifying the location of the marker and the location and orientationof the target, the data processing unit being configured to compare thevisual diagnostic data to the location and spatial orientation of thetarget within the body relative to the plurality of sensors and toidentify a target isocenter within the target prior to application ofradiation treatment to the target.
 51. A radiation treatment systemusable to deliver ionizing radiation to a selected target within a body,comprising: a movable gantry configurable to deliver the ionizingradiation at a treatment isocenter remote from the gantry; a markerfixable at a position relative to the target within the body, the markerbeing excitable by an external source to produce a measurable markersignal while in the body; sensors spaced apart in a known geometryrelative to each other and positioned to measure the marker signal, eachsensor being configured to measure the marker signal and provide amarker measurement signal; a linear accelerator reference device mountedon the gantry at a known position relative to the machine isocenter; anda computer controller coupled to the sensors to receive the markermeasurement signals and configured to use the marker measurement signalsto determine the location of the target volume and a target isocenter inthe target volume relative to the sensors, and the computer controllerbeing coupled to the reference device and configured to identify thelocation of the target isocenter relative to the machine isocenter. 52.The radiation treatment system of claim 51, further comprising a patientsupport structure shaped and sized to support the body in which themarker is implanted, and the sensors are mounted in a fixed locationrelative to a portion of the patient support structure.
 53. Theradiation treatment system of claim 51, further comprising a monitoringsystem coupled to the computer controller, the monitoring system havinga feedback portion configured to provide feedback information about theposition of the machine isocenter and the target isocenter relative toeach other.
 54. The radiation treatment system of claim 43 wherein thecomputer controller and monitoring system are configured to identify anddisplay real time movement of the target and machine isocenters relativeto each other.
 55. The radiation treatment system of claim 53, whereinthe computer controller contains imaging data identifying the locationof the marker and the location and orientation of the target, thecomputer controller being configured to compare the imaging data to thelocation and spatial orientation of the target within the body relativeto the plurality of sensors and to identify a target isocenter withinthe target prior to application of radiation treatment to the target.56. A radiation target alignment system usable with a radiation deliverysource that delivers selected doses of radiation to a selected target ina body, comprising: an imaging system configured to obtain image data ofthe target and at least one marker positioned within the body, and todefine a simulated target model having a spatial relationship andorientation within the body using the image data; a marker implantablein or on the body at a selected position relative to the target, themarker being excitable by an external source to produce a measurablesignal while in the body; a plurality of sensors spaced apart in a knowngeometry relative to each other and positioned to identify the signalfrom the marker in the body, each sensor being configured to measure themarker signal and provide a marker measurement signal; a data processingunit coupled to the sensors to receive the marker measurement signal forthe marker, the data processing unit being configured to use the markermeasurement signal and the image data to determine an actual targetmodel of the target's actual location within the body relative to theplurality of sensors, and to identify a target isocenter within thetarget, the data processing unit being configured to compare and alignthe actual target model and the simulated target model in preparationfor radiation treatment of the target.
 57. The radiation targetalignment system of claim 56 wherein in the marker is one of a pluralityof markers attachable to the body, and each marker generates a uniquemeasurable signal different from the other marker signals.
 58. Theradiation target alignment system of claim 57 wherein the plurality ofmarkers includes at least three markers.
 59. The radiation targetalignment system of claim 57 wherein the plurality of markers areaxially misaligned with each other.
 60. The target locating and trackingsystem of claim 56 wherein the marker is one of a plurality of markers,and the markers each being axially misaligned with each other, the dataprocessing unit being configured to identify a three-dimensional spatialposition as well as orientation of the target relative to the pluralityof sensors.
 61. The radiation target alignment system of claim 56 withthe radiation delivery source adapted to deliver radiation to a machineisocenter spaced apart from the radiation delivery source, wherein thedata processing unit is configured to identify the location of themachine isocenter relative to the actual target isocenter.
 62. Theradiation target alignment system of claim 56, further comprising amonitoring system coupled to the data processing unit, the monitoringsystem having a display portion configured to display the position ofthe machine isocenter and the actual target isocenter relative to eachother.
 63. The radiation target alignment system of claim 62 wherein thedata processing unit and monitoring system are configured to identifyand display real time movement of the target and machine isocentersrelative to each other.
 64. An adjustable patient support assembly foruse with a radiation delivery system that delivers radiation to aselected target in a body, the radiation being delivered to a machineisocenter spaced apart from the radiation delivery source, comprising: abase; a support structure attached to the base; sensors spaced apartfrom each other in a known geometry relative to each other and coupledto the base, the sensors being positioned to measure a signal from anexcitable marker implantable in the body at a selected position relativeto the target, each sensor being configured to provide signalmeasurement data; a data processing unit coupled to the sensors toreceive the signal measurement data for the marker, the data processingunit being configured to use the signal measurement data for the markerto determine the location of the target and a target isocenter in thetarget relative to the sensors, the data processing unit beingconfigured to identify the location of the target isocenter relative tothe machine isocenter; and a movement control device connected to thesupport structure to selectively move the support structure relative tothe base and the sensors, the movement control device coupled to thedata processing unit and being movable in response to the informationfrom the data processing unit to position the target isocenterco-incident with the machine isocenter.
 65. A method of identifying andtracking a selected target in a body for application of radiation to thetarget from a radiation delivery source, comprising: determining ageneral location of the target in the body; implanting a marker in thebody at a selected position relative to the target, the marker beingexcitable by an external excitation source to produce an identifiablemarker signal while in the body; exciting the implanted marker with theexternal excitation source to produce the identifiable marker signal;measuring the marker signal from the implanted marker with sensorsexterior of the body, the sensors being positioned at a known geometryrelative to each other; determining a target isocenter in the targetwithin the body based upon the measurements from the sensors of themarker signal; determining a position of a reference device relative tothe plurality of sensors, the reference device being located at a knowngeometry relative to the radiation delivery device; determining thelocation of a machine isocenter relative to the plurality of sensorsbased upon the position of the reference device; positioning the bodyrelative to the radiation delivery device with the target isocenterbeing coincident with the machine isocenter; and applying radiation fromthe radiation delivery device to the machine isocenter and the target atthe target isocenter.
 66. The method of claim 65, further comprising:implanting a plurality of markers in the body at a selected positionsand orientations relative to the target, each marker being excitable bythe external excitation source to produce an identifiable marker signalunique to the respective marker; exciting the implanted markers with theexternal excitation source to produce the identifiable unique markersignals; measuring the marker signals from each of the implanted markerswith the sensors exterior of the body; determining a location of thetarget isocenter in the target within the body based upon themeasurements from the sensors of the marker signals.
 67. The method ofclaim 65, further comprising determining the location and orientation ofthe target in the body relative to the sensors.
 68. The method of claim65 wherein the marker generates the marker signal having a signalstrength and measuring the marker signals includes measuring the markerstrength with each sensor.
 69. The method of claim 65, furthercomprising providing a monitoring system coupled to a computercontroller and providing feedback from the computer controller to themonitoring system about the position of the machine isocenter and thetarget isocenter relative to each other.
 70. The method of claim 69wherein the monitoring system includes a visual display portion, andproviding feedback includes providing a visual representation on thevisual display portion of the positions of the target and machineisocenters relative to each other.
 71. The method of claim 65, furthercomprising implanting at least three markers in the body at selectedpositions relative to the target, each of the at least three markersbeing axially misaligned with each other.
 72. The method of claim 65further comprising positioning the body at a selected location generallyadjacent to the radiation delivery source, and wherein measuring themarker signal, determining a location of the target isocenter,determining the location of a machine isocenter, and positioning thebody relative to the radiation delivery device so the target isocenterbeing coincident with the machine isocenter are performed in real timeprior while the body is positioned at the selected location generallyadjacent to the radiation delivery device.
 73. The method of claim 65wherein the target is a tumor, and implanting the marker includesimplanting the marker in or immediately adjacent to the tumor, anddetermining the location of the target isocenter includes determining alocation of the target isocenter in the tumor.
 74. The method of claim65 wherein the sensors are mounted to a movable support table thatsupports the body generally adjacent to the radiation delivery device,and positioning the body includes moving a portion of the support tablerelative to the radiation delivery device and to the sensors to alignthe target isocenter with the machine isocenter.
 75. The method of claim65, further comprising monitoring the position of the target isocenterrelative to the machine isocenter in real time during irradiation of thetarget, and interrupting the irradiation of the target if the targetisocenter moves out of alignment with the machine isocenter.
 76. Amethod of delivering radiation therapy on a selected target within abody, comprising: implanting a marker in the body at a selected positionrelative to the target, exciting the implanted marker with an excitationsource external of the body to produce an identifiable marker signal;measuring the marker signal from the implanted marker with sensorspositioned exterior of the body and at a known geometry relative to eachother; determining a target isocenter in the target within the bodybased upon the measurements from the sensors of the marker signal;determining the location of a machine isocenter of a radiation deliveryassembly relative to the plurality of sensors based upon the position ofthe reference device and relative to the target isocenter; positioningthe body relative to the radiation delivery device so the targetisocenter is co-incident with the machine isocenter; applying radiationfrom the radiation delivery device to target at the target isocenter andthe machine isocenter; and monitoring in real-time the actual positionof the target isocenter relative to the machine isocenter duringapplication of the radiation to the target.
 77. A radiation treatmentplanning method for establishing a therapeutic procedure for deliveringionizing radiation to a selected target, comprising: obtaining imagingdata of a selected target within a body; implanting an excitable markerin the body at a selected location relative to the target; exciting theimplanted marker with the external excitation source to produce theidentifiable marker signal from the marker while in the body; measuringthe marker signal from the implanted marker with a plurality of sensorsexterior of the body, the sensors being positioned at a known geometryrelative to each other; determining a shape, and spatial orientation ofthe target within the body from the imaging data; determining a targetisocenter in the target within the body based upon the measurements fromthe sensors of the marker signal; and developing a radiation dosage anddelivery protocol for irradiating the target at the target isocenterbased upon the shape and spatial orientation of the target.
 78. Themethod of claim 77, further comprising: positioning the body with thetarget and implanted marker therein at a selected position relative to aradiation delivery assembly, the radiation delivery assembly beingconfigured to selectively deliver focused radiation to a targetisocenter spaced apart from the radiation delivery assembly; determiningthe location of a machine isocenter relative to the plurality ofsensors; positioning the body relative to the radiation delivery devicewith the target isocenter being substantially co-incident with themachine isocenter; and delivering the radiation from the radiationdelivery assembly to the machine isocenter and to the target at thetarget isocenter.
 79. The method of claim 77, further comprisingdefining a three-dimensional simulated target model with a selectedposition and orientation relative to the body based upon the imagingdata; and defining an three-dimensional actual target based upon themeasurements of the marker signals, providing a feedback device thatprovides feedback information about the location and orientation of thesimulated target model and the actual target model, and moving the bodyto align orientation of the target and actual models prior to thedelivery of the radiation to the target.
 80. A method of positioning abody relative to a radiation delivery device for delivery of radiationto a target within the body, comprising: positioning the body on amovable support assembly; exciting an excitable marker with anexcitation source exterior of the body, the marker being implantedwithin the body at a selected position relative to the target, theexcited marker providing an identifiable marker signal; measuring themarker signal from the implanted marker with a plurality of sensorsexterior of the body, the plurality of sensors being positioned at aknown geometry relative to each other and relative to the supportassembly; determining a target isocenter in the target within the bodybased upon the measurements from the sensors of the marker signal;determining the location of a machine isocenter relative to theplurality of sensors based upon the position of the radiation deliveryassembly; comparing the location of the target isocenter with thelocation of the machine isocenter; and moving a portion of the supportportion and the body together relative to the machine isocenter toposition the target isocenter co-incident with the machine isocenter.81. The method of claim 80, wherein the plurality of sensors areconnected to the support assembly, and moving the portion of the supportportion includes moving the portion of the support portion and the bodytogether relative to the plurality of sensors.